Electron device



July 9, 1940. BANKS 2,207,503

ELECTRON DEVICE Filed June 3, 1938 INVENTOR.

GEORGE LOW/N BAA/KS BY $2 7 M-u-M/ ATTORNEY.

Patented July 9, 1946 UNITED STATES ELECTRON DEVICE George Baldwin Banks, Billericay, England, assignor to Radio Corporation of America, a corporation of Delaware Application June s, 1938, Serial No. 211,476 In Great Britain June 5, 1937 4; Claims.

The present invention relates to electron multipliers and more particularly to grid controlled electron multiplier arrangements. The main object of the invention is to provide improved grid .5 controlled electron multiplier arrangements capable of responding to or amplifying very small voltage fluctuations.

Hitherto it has not been found possible to amplify very small voltage fluctuations by means of grid controlled electron multipliers. The reasons for this difilculty will best be understood by considering a typical triode arrangement having a mutual conductance of 2 milliamperes per volt and a grid voltage (Ve-abscissae)anode current (Le-ordinates) characteristic as shown conventionally in the accompanying figure I; i. e. such that a suitable working point. (P) on the characteristic corresponds with a negative potential on the control grid of 0.5 of 'a volt and an anode current of 1 milliampere and a small fluctuating voltage of say, 1 millivolt, applied to the control grid results in the anode current fluctuating between 1 microampere below and 1 microampere above the steady Value of 1 milliampere. If, now, secondary emitting electrodes were 'interposed in such a triode between the cathodegrid system and the anode so that the original electronic stream were amplified one thousand times before reaching the anode, both the anode steady current and the anode current fluctuations would be increased one thousand fold, the steady current being accordingly increased to 1 ampere and the fluctuations to 2 milliamperes. This steady current value would, for various practical reasons, render the tube quite unsuitable for use as an amplifier for very small voltage fluctuations. Up to the present, in fact, it has not been found possible to take advantage of secondary emission to produce a thermionic Valve with a high value of mutual conductance, the limit being about thirty milliamperes per volt.

The present invention seeks to avoid the above difficulty and limitation, and, as will be seen later, this object is achieved, in carrying out the invention, by eliminating the unwanted steady current before it has become unduly large.

According to this invention an electron multiplier arrangement comprises in combination a plurality of cascaded electron multiplier systems each comprising a primary cathode, an output electrode, at least one secondary emitting electrode therebetween and a control electrode, alternating current coupling means to suppress direct current between the output electrode of each system and the control electrode of the system next in the cascade chain, an output or utilization circuit fed from the output electrode of the last system, and an input circuit arranged to feed into the control electrode of the first system.

Two embodiments of the invention are illustrated in the accompanying drawing in Figures 2 and 3, while Fig. 1 shows a characteristic curve of a multiplier for purposes of explaining the invention. I

Referring to Figure 2 the arrangement therein employed comprises two electron multiplier tubes Vi and V2 each as known per se and comprising thermionic cathode Cl or C2'suitably disposed behind a control electrode GI or G2, a number of co planar secondary emitting electrodes Si or S2 (in the tubes shown there are four in each tube), a number of co-planar field plate electrodes Fl or F2 arranged in a plane parallel to the plane of the secondary'emitting electrodes one opposite the control electrode and one opposite each secondary emitting electrode, and a collector electrode Al or A2 arranged beyond that secondary emitting electrode which is most remote from the cathode and at right angles to and between the field and secondary emitting electrode planes. The secondary emitting electrodes in each tube are maintained at successively increasing positive potentials in a direction away from the cathode, as also are the field-plate electrodes and each of thelatter electrodes is at a higher positive potential than the emitting electrode which it faces. The potential supplyarrangements shown are of the known type in which each secondary emitting electrode is directly connected to the immediately preceding field electrode, the potential supply leadsbeing marked LI or L2. Each secondary emission multiplier is subjected to an electron deflecting and focusing field system, which may be either magnetic and/or electrostatic so as to cause the electron stream from the primary cathode to pass in more or less cycloidal paths to the first secondary emitting electrode, the secondary electrons from which bombard the next secondary emitting electrode, and so on until-the collecting electrode is reached. The electron deflecting and focusing system may be of any known kind to produce this result as in the usual way. The number of secondary emitting electrodes in and the general arrangement of each tube may, for instance, be such thatthemutual conductance is 30 milliamperes per volt. The collecting electrodes of the tubes are connected to points +HTI, +HT2 of suitable positive potential through high resistances RI, R2 and the grids GI G2 are suitably negatively biased by sources GBI, GB2. The collecting electrode AI of the first tube VI is connected through a blocking and coupling condenser KI to the control grid G2 of the second tube V2 and the collecting electrode A2 of the second tube is similarly coupled through a condenser K2 to a suitable utilization system (not shown). There may be any number of tubes, each of small mutual conductance (up to about 30 milliamperes per volt) coupled in cascade in the same manner as are the tubes VI V2 the last tube being similarly coupled to the utilization circuit. The small fluctuating voltage to be amplified is applied at IN between the grid GI and cathode CI of the first tube VI across an input resistance IRI and results in an amplified fluctuating voltage appearing across the high resistance RI in the collecting electrode circuit of the said tube. This amplified fluctuating voltage is similarly applied across resistance 1R2 to the control grid G2 of the second tube V2 through the blocking and coupling condenser KI which eliminates the steady direct current. If, in an arrangement as shown in Figure 2 the mutual conductance of each tube is 30 milliamperes per volt and RI and R2 are 10,000 ohms each the voltage amplification (voltage at the output terminals OUT divided by the voltage at the input terminals IN) will be The several multiplier structures may, if desired, be assembled within a single envelope and a common electron deflecting and focusing field system and a common power supply may be provided as is well known in the prior art and shown in Patent No. 2,078,304 issued to Zworykin et al. on April 27, 1937. In such a case corresponding field plate and secondary emissive electrodes respectively of the two systems may be directly connected together within the envelope.

Figure 3 shows a modification suitable for use as a radio receiver. Here tube VI is fed from a receiving aerial AN and amplifiers at radio frequency while the second tube V2 is a combined detector and audio amplifier detection being effected at the grid G2 of the second multiplier by suitably biasing the grid to the curved portion of its characteristic. In Fig. 3 TCI is an input tuned circuit, TC2 is a second radio frequency tuned circuit replacing the resistance RI of Fig. 1 and output from the second tube is taken by the transformer coupling by a transformer TR to the utilization device, which is shown as a loudspeaker LS.

Having described my invention, what I claim is:

1. A signal amplification system comprising a plurality of electron multiplier tubes each adapted to amplify the effect of impressed A. C. signals to a predetermined degree whereat the D. C. component at the output of each stage increases to a predetermined degree relative to the amplified A. C. component, an output load circuit connected to the last of said plurality of multiplier tubes, and a coupling between the successive independent multiplier tubes to suppress the D. C. component of the amplified energy from the preceding multiplier stage and for permitting the A. C. component to pass substantially unattenuated to the succeeding multiplier stage.

2. A signal amplifying system comprising an input circuit for receiving modulated signal energy, an output load circuit, a pair of electron multiplier tubes, means for energizing one of the tubes under the control of the signal energy in the input circuit, said energized tube being adapted to amplify the impressed modulated signal energy to a predetermined degree wherein the magnitude of the direct current component becomes relativly great relative to the alternating current component of the signal, a coupling circuit including means to suppress direct current components for supplying the amplified energy from the signal energized electron multiplier to the second electron multiplier, said second electron multiplier also being adapted to amplify the signal energy to a predetermined degree, and means for connecting the load circuit to receive the amplified modulated signal energy from the second electron multiplier tube to the exclusion of undesired amplified direct current components.

3. A signal amplification system comprising a pair of static electron multiplier tubes, an output electrode for each of the multiplier tubes, a load circuit connected to receive the output energy from the second of said multiplier tubes, means to vary the A. C. component of amplification in the first of said multiplier tubes under the control of signal energy to be amplified, each of said amplifier tubes being adapted to amplify the sig nal energy to a predetermined degree and simultaneously amplify undesired direct current components of said energy to such an extent that the relative magnitude of the undesired D. C. component becomes large relative to the amplified signal energy, a coupling circuit connecting the output electrode of the first of said multiplier tubes to the input of the second of said multiplier tubes, said coupling circuit including means for transferring the amplified A. C. component from said first multiplier tube to the second of said multiplier tubes substantially unattenuated and for suppressing the undesired D. C. component, said second electron multiplier also being adapted to amplify the signal energy supplied thereto in a manner substantially identical to the first of said tubes, and means for supplying the output energy from the second of said multiplier tubes to the load circuit and simultaneously again suppressing any undesired D. C. components of the amplified energy.

4. A signal amplifying system comprising electron multiplying means including a substantial number of amplification stages of which each stage amplifies an electron flow in accordance with a predetermined secondary emission ratio for each stage and the amplified undesired D. C. component becomes relatively greater per stage than the desired A. C. component, means to control the electron flow in the initial stage in accordance with signal energy to be amplified, means interposed between at least some of the successive stages of amplification for suppressing the undesired D. C. component and for passing the desired A. C. component to succeeding stages substantially unattenuated, an output load circuit, and means comprising an A. C. coupling for supplying the amplified energy of the last or" said multiplier stages to the load circuit.

GEORGE BALDWIN BANKS. 

